1. Field of the Invention
The present invention relates to an electronic component such as, for example, a piezoelectric component and, more particularly but not exclusively, to a surface-mount type electronic component. The present invention also relates to a method of producing such an electronic part.
2. Description of the Related Art
A surface-mount type electronic component, specifically a piezoelectric component, of the type shown in FIGS. 1 and 2 is known. This electronic component incorporates an element 4 which makes use of piezoelectric vibration (referred to as xe2x80x9cpiezoelectric elementxe2x80x9d). The piezoelectric element 4 includes electrodes 4a and 4b disposed on upper and lower major surfaces thereof and is arranged to vibrate in a longitudinal vibration mode. Pattern electrodes 2 and 3 are provided on a substrate 1 which supports the piezoelectric element 4. The lower electrode 4b disposed on the lower major surface of the piezoelectric element 4 is connected and fixed to a first one 2 of the pattern electrodes by a conductive adhesive 5. The upper electrode 4a disposed on the upper major surface of the piezoelectric element 4 is connected to the other pattern electrode 3 by a wire 6. A cap 7 is attached to the upper surface of the substrate 1 so as to cover and seal the piezoelectric element 4.
In the piezoelectric component shown in FIG. 1, the upper electrode 4a of the piezoelectric element 4 and the pattern electrode 3 disposed on the substrate 1 are connected to each other by a wire bonding technique. It has been difficult, however, to optimize the wire-bonding process and resulting structural arrangement due to the difference in height or vertical location between the electrode 4a of the piezoelectric element 4 and the pattern electrode 3 disposed on the substrate 1.
When a capillary is moved while the wire 6 is being connected to one of these electrodes 3 and 4a, it is necessary to optimize the length of feed of the wire 6. If a feed length of the wire 6 is too small, the wire 6 may contact an edge of the piezoelectric element 4 as shown in FIG. 3, resulting in troubles such as cutting of the wire 6 or impairment of the electrical characteristics of the piezoelectric element 4. Conversely, if the feed length of the wire 6 is too large, this causes problems such as the wire 6 sagging downwardly as shown in FIG. 4, with the result that the wire 6 contacts the piezoelectric element 4 to impair electrical characteristics of the element 4.
For these reasons, mass-production of electronic components requiring wire bonding involves great manufacturing difficulty and experiences significant fluctuation of the quality.
Another problem is that the size of the electronic component must be large because of the need to provide a space between the substrate 1 and the cap 7 for accommodating the wire 6 which interconnects the upper electrode 4a of the piezoelectric element 4 and the pattern electrode 3 disposed on the substrate 1.
In the meantime, electronic components having lead terminals suffer from the following problem. In general, an electronic component, specifically of the type in which a circuit element is sealed with a resin without being constrained by the resin, has such a structure as that disclosed in Japanese Patent Publication No. 1-48695, wherein lead terminals are electrically connected to the corresponding electrodes of the circuit element and, after the circuit element is enclosed in a case with the lead electrodes extending externally through openings formed in the case wall, these openings are sealed by a sealing resin.
This type of structure, however, requires that different design configurations of the openings be provided in conformity with the shapes of the lead terminals, at the time of design of the products. In addition, it is necessary to apply a sealing resin to each of the openings in a one-by-one fashion. This causes an impediment to mass-production of the electronic parts, thus raising the costs of production.
Prior to the application of the sealing resin, since the lead terminals are directly connected to the circuit element, any load or external force tends to be directly transmitted to the circuit element, often resulting in breakage or cracking of the circuit element especially when the circuit element is a fragile one such as a piezoelectric element. Consequently, throughput is lowered and the number of acceptable components manufactured is substantially reduced.
The preferred embodiments of the present invention provide an electronic component which allows for easy electrical connection between a circuit element and an electrode pattern on a substrate supporting the circuit element, thus providing stabilization of quality of the electronic components at reduced costs, as well as reduction in the size of the electronic component. The preferred embodiments of the present invention also provide a method for producing such an electronic component having these advantages.
The preferred embodiments of the present invention also provide an electronic component which is easily mass-producible at low costs and which has a structure which allows for completely sealing a circuit element of the electronic component while suppressing an application of load to the circuit element to prevent damage to the circuit element and deterioration of the electrical characteristics of the electronic component.
According to one preferred embodiment of the present invention, an electronic component comprises: an insulating substrate having an electrode pattern provided thereon; a circuit element mounted on the insulating substrate; and a cap bonded to the substrate so as to cover and seal the circuit element; wherein a conductive portion is provided on at least the inner surface of the cap, the conductive portion being connected to an electrode of the circuit element and also to the electrode pattern on the substrate, whereby the electrode of the circuit element is electrically connected to the electrode pattern on the substrate through the conductive portion of the cap.
In accordance with the preferred embodiments of the present invention, the cap preferably is used as a part of the electrical connection, for the purpose of achieving electrical connection between an electrode of the circuit element and the electrode pattern provided on the substrate. This connecting method considerably facilitates the establishment of an electrical connection between the circuit element and the electrode pattern on the substrate, as compared with the wire bonding method which has previously been used, thereby contributing to reduction in the costs and stabilization of the quality of the electronic component being manufactured. Furthermore, the size of the cap and, hence, the size of the whole electronic component, can be reduced because of elimination of the necessity for providing a wiring space which has previously been required in order to establish electrical connection between the electrode on the surface of the circuit element and the electrode on the substrate.
The conductive portion of the cap may be provided by forming the whole cap from a metallic material such as aluminum, copper or the like. Alternatively, the cap may be formed from an insulating material such as ceramics or resin, and a conductive film may be disposed at least on the inner surface of the cap by a suitable technique such as sputtering, evaporation deposition, printing or the like.
When the circuit element is a piezoelectric element which is provided at its upper and lower major surfaces with electrodes and which makes use of piezoelectric vibration, the arrangement is preferably such that the connection to the conductive portion of the cap is made at a region of the electrode on the upper surface of the circuit element near a nodal point of the vibration. Such an arrangement does not inhibit vibration of the piezoelectric element and, therefore, does not impair the electrical characteristics of the electronic component, because the conductive material which interconnects the conductive portion of the cap and the electrode on the surface of the piezoelectric element is preferably located in a region near the nodal point which is free of vibration.
In general, there are a plurality of vibration modes of piezoelectric vibration, such as longitudinal vibration mode, radial vibration mode, and so forth. In each of these modes, the nodal point is located at the centers of the upper and lower surfaces of the piezoelectric substrate. It is therefore preferred that the piezoelectric element is fixed to the substrate substantially at the approximate center of the lower surface thereof and is connected to the cap inner surface substantially at the approximate center of the upper surface thereof.
The electronic component in accordance with the preferred embodiments of the present invention is preferably but not exclusively a piezoelectric component.
According to another preferred embodiment of the present invention, there is provided a piezoelectric component, comprising: a substrate having an electrode disposed on the upper surface thereof; a piezoelectric element having electrodes disposed on upper and lower major surfaces thereof and mounted on the substrate, the electrode on the lower surface of the piezoelectric element being electrically connected to the electrode on the substrate; and a cap made of a metallic material and bonded to the substrate so as to cover and seal the piezoelectric element; and a conductive wire provided on the electrode on the upper surface of the piezoelectric element; the cap being placed so as to cover the piezoelectric while making contact at the inner surface thereof with the conductive wire, whereby the electrode on the upper surface of the piezoelectric element is electrically connected to the cap through the conductive wire.
According to still another preferred embodiment of the present invention, there is provided a method of producing a piezoelectric component of the type having a substrate with an electrode disposed thereon, a piezoelectric element having electrodes provided on upper and lower surfaces thereof and mounted on the substrate, and a cap bonded to the substrate so as to cover and seal the piezoelectric element, the method comprising the steps of: fixing the piezoelectric element on the substrate such that the electrode on the lower surface of the piezoelectric element is connected to the electrode of the substrate; fixing a conductive wire to the electrode on the upper surface of the piezoelectric element; applying a conductive adhesive to the portion of the inner surface of the cap for contacting with the conductive wire; applying a sealing adhesive to an opening of the cap; placing the cap on the substrate such that the conductive wire contacts the inner surface of the cap to cause a portion of the conductive wire to contact with the conductive adhesive; and simultaneously curing the sealing resin and the conductive adhesive.
In these preferred embodiments of the present invention, electrical connection between the electrode disposed on the upper surface of the piezoelectric element and the cap is preferably achieved by a wire which is fixed on the electrode on the upper surface of the piezoelectric element and which is pressed against the inner surface of the cap. The wire may be formed by a known technique such as that used in wire bonding technique. If the position at which the wire is fixed to the piezoelectric element is determined to be the vibration-free portion of the piezoelectric element, there is no substantial risk that the vibration is impeded, unlike the case where a conductive adhesive used as the connecting material is spread over a wide area to impede vibration of the piezoelectric element. In addition, any thermal stress produced as a result of difference in thermal expansion between different materials is effectively absorbed by the elastic nature of the wire, so that electrical conduction can stably be maintained with a high degree of reliability. The elastic nature of the wire also serves to absorb any fluctuation in the size of the gap between the cap and the piezoelectric element, which provides a greater tolerance in the administration of dimensions.
Preferably, the wire has a loop-like form and is preferably fixed at both ends to the electrode on the upper surface of the piezoelectric element. Such a loop shape provides a large elasticity so as to ensure stable contact between the cap and the wire. The loop-shaped wire can withstand long use with reduced risk of cutting or sagging down, thus offering a high degree of reliability and eliminating the problems of the prior art wire connections. The wire may be formed by using a known technique such as that used in a wire bonding method. Since the points on the electrode on the upper surface of the piezoelectric element to which the ends of the loop-shaped wire are connected are almost at the same vertical level, an optimum condition for achieving electrical connection can be determined without difficulty.
Preferably, the whole cap is made of a metallic material having excellent electrical conductivity, such as aluminum, copper or the like.
The piezoelectric element may be adapted to vibrate in any vibration mode. It is, however, preferred that the wire is fixed to a portion of the piezoelectric element which is free of vibration or a region near such a vibration-free point. In case of a piezoelectric element having a nodal point, e.g., a piezoelectric element using longitudinal vibration mode or radial vibration mode, it is recommended that the wire is fixed to such a nodal point. Similarly, the portion of the lower side of the piezoelectric element at which the element is fixed to the substrate electrode should be a portion which is free of vibration.
Although electrical connection can be achieved merely by bringing the cap into contact with the wire, it is preferred that a conductive adhesive be applied to the portion of the cap inner surface where the contact with the wire occurs, if a specifically low level of resistance and high level of reliability are desired. In such a case, the amount of the conductive adhesive to be applied should be determined such that the adhesive contacts with the wire alone, i.e., the adhesive does not contact the piezoelectric element, in order to avoid restriction of vibration of the piezoelectric element.
Preferably, the electrode on the substrate extends externally and a first lead terminal is connected to this externally led portion of the substrate electrode, while a second lead terminal is connected and fixed to the outer surface of the cap. In this case, the electrode disposed on the upper surface of the piezoelectric element is preferably directly connected to the lead terminal through the cap, without using the intermediary of the electrode on the substrate, whereby a piezoelectric component of the lead-terminal type having a simple construction for external connection can be obtained.
It is also possible to obtain a surface-mount type piezoelectric component, by forming an input/output electrode and a grounding electrode on the substrate and externally extending the electrodes through a region where the cap is bonded, with the input/output electrode connected to the electrode on the lower side of the piezoelectric element, while connecting the cap to the grounding electrode.
According to a further preferred embodiment of the present invention, there is provided an electronic part, comprising: an insulating substrate having pattern electrodes provided thereon; a circuit element mounted on the surface of the substrate and having electrodes electrically connected to the pattern electrodes; a cap bonded to the surface of the substrate so as to cover and seal the circuit element; and lead terminals electrically connected to portions of the pattern electrodes which extend externally from the cap; wherein the cap is made of an electrically conductive material and is electrically connected to one of the electrodes of the circuit element and with at least one of the lead terminals.